It is well established in the art to produce ophthalmic lenses, more specifically hard and soft contact lenses, in an automated manufacture process with reusable molds. In mass production of contact lenses, specifically so-called disposable lenses, a large number of contact lenses must be manufactured in a relatively short period of time. In an advantageous method of mass production, a lens forming material, e.g., a polymer or prepolymer solution is introduced into a female mold half, the casting mold is closed by the respective male mold half and then the lens forming material is polymerized and/or cross-linked e.g. with ultraviolet (UV) light. Such mass production of contact lenses, which is usually performed in a closed loop process, is described, e.g., in WO 98/42497. Suitable polymers formed by photochemical polymerization of suitable prepolymers include polymers based on polyvinyl alcohols (PVA) or silicone hydrogels (SiHy) as well as based on polyethylene glycols (PEG).
During the UV light induced polymerization and/or cross-linking of the lens forming material within the molds the UV light in the respective zones which are outside of the areas required for contact lens production is masked. Thus, due to this spatial limitation of the irradiated UV light only the unmasked portion of the lens forming material in the mold cavity is hardened, whereas excess material e.g. in an overflow of the mold remains attached to the lens as “flash”. In order to obtain fault-free lenses these residues of non-polymerized and/or non-cross-linked lens forming material, the “flash” must be separated from the molded lens. This separation is supported by a proper sealing of the mold halves and by a very careful shaping of the mold separation planes, in particular in the edge region of the mold cavity which defines the lens edge. The automated manufacture process is also called “full mold process” because there is no working of the lens edge required after the molding of the lens.
In order to remove a lens from the mold the mold is opened by moving the mold halves away from each other. During the opening of the mold non-polymerized and/or non-cross-linked lens forming material may reach the exposed surface, usually the front surface, of the lens and adhere thereto. Thus, in particular the peripheral region of the formed lens may be soiled. In a known manufacture process there is a cleaning step for the lens provided after the opening of the mold, in which the lens is flushed with a flushing medium, usually deionised water (VE water). In spite of this flushing step there may still occur a certain number of lenses, which still contain residues of non-polymerized and/or non-cross-linked lens forming material in the peripheral region of the exposed (front) surface. These residues are only detected at the optical inspection of the lenses prior to packaging and may result in a considerable number of rejected lenses. Certain lens forming materials are flushed even with an organic solvent, in order to remove the residues of non-polymerized and/or non-cross-linked material from the lens surface. It is to be noted, though, that lenses made from these materials and treated with organic solvents must be thoroughly rinsed and washed in order to remove any residues of the organic solvent from the lenses.
It is therefore an object of the present invention to provide a method by which excess lens forming material, which is non-polymerized and/or non-cross-linked, may reliably be removed from the exposed surface of a molded lens. A method shall be provided which enables a cleaning of the exposed lens surface without the use of organic solvents. A method and a device shall be provided, which may be easily integrated in known production lines for ophthalmic lenses, such as contact lenses.
These and still further objects are met by a method of separating excess lens forming material from a molded ophthalmic lens, more specifically a contact lens, which comprises the method steps listed in patent claim 1. The objects are also met by an apparatus for carrying out the method which comprises at least the features claimed in the independent apparatus claim. Further improvements of the invention and preferred embodiments are subject of the dependent claims.